Fire control system

ABSTRACT

A stabilization system for the turret and cradle of an armored vehicle for maintaining the orientation of a weapon supported therein in an inertial frame of reference, thereby correcting for disturbances of the hull of the vehicle caused by steering in a direction other than directly at the desired target as well as for variations in pitch, roll and yaw caused by movement over uneven terrain. Two rate gyros mounted on the cradle, a rate gyro on the hull cooperate in pairs to provide inertial control signals in elevation and traverse to modify servo loop dynamic response and to maintain a stabilized position with respect to a preselected frame of reference. In each axis signals developed by integration of one cradle rate gyro output, by a servo valve position transducer, a tachometer coupled to the hydraulic motor and a paired rate gyro, and by differentiation of the tachometer and paired rate gyro output are combined with the manually introduced signal derived from the gunner&#39;&#39;s station for control of the servo valve and the motor for positioning either the turret or the cradle supporting the weapon. Automatic drift compensation is included for correction of electronic offsets and mechanical variances within the system, consisting of a potentiometer mechanically coupled into the system at the option of the operator to produce a continuous signal, thereby providing correction to the combined control signal applied to the servo valve.

United States Patent Taylor et al.

[ Oct. 29, 1974 FIRE CONTROL SYSTEM [75] Inventors: John E. Taylor,Kalamazoo; Jack M.

Brandstadter, Royal Oak, both of Mich.

[73] Assignee: Pneumo Dynamics Corporation,

Cleveland, Ohio 22 Filed: Sept. 28, 1972 21 Appl. No: 292,934

Primary Examiner-Stephen C. Bentley Attorney, Agent, or Firm--Donnelly,Maky, Renner & Otto [57] ABSTRACT A stabilization system for the turretand cradle of an 46 WORTH POT.

WEAPON armored vehicle for maintaining the orientation of a weaponsupported therein in an inertial frame of reference, thereby correctingfor disturbances of the hull of the vehicle caused by steering in adirection other than directly at the desired target as well as forvariations in pitch, roll and yaw caused by movement over eqeveat reia-TWO rate reemoqm d on the ratl e a rate gyro on the hull cooperate inpairs to provide inertial control signals in elevation and traverse tomodify servo loop dynamic response and to maintain a stabilized positionwith respect to a preselected frame of reference. In each axis signalsdeveloped by integration of one cradle rate gyro output, by a servovalve position transducer, a tachometer coupled to the hydraulic motorand a paired rate gyro, and by differentiation of the tachometer andpaired rate gyro output are combined with the manually introduced signalderived from the gunners station for control of the servo valve and themotor for positioning either the turret or the cradle supporting theweapon. Automatic drift compensation is included for correction ofelectronic offsets and mechanical variances within the system,consisting of a potentiometer mechanically coupled into the system atthe option of the operator to produce a continuous signal, therebyproviding correction to the combined control signal applied to the servovalve.

12 Claims, 4 Drawing Figures SERVOVALVE PATENTED I18? 29 89M 45 DRIFTDRIFT POT.

2 WEAPON POS. GYRO j CONTROL 32 POT. ssRvovAL\ E" 35 2e a 34 2ND STAGEvewcnv LVDT 36 4% TAOHOMETER m 5r- HULL 42 i E cvno FIRE CONTROL SYSTEMThis invention relates to inertial guidance and stabilization systemsand more particularly to the stabilization system for the weapon of anarmored vehicle subject to movement in plural axes.

Many systems have been devised for the powered control and stabilizationof weapons and the like in military vehicles, for example, naval vesselsand aircraft which mount rotatable turrets for the orientation ofweapons supported thereby, however significantly different problems areencountered in the application of these systems to land orientedvehicles including the relatively high amplitudes and frequenciesoccurring in movement and the heretofore unappreciated degree ofstructural resonances encountered which affect the accuracy and responseof such systems.

Difficulties are encountered in providing a sufficiently wide dynamicrange for the servo system as well as providing for the necessaryfrequency response in order to be sensitive to a wide range ofconditions, so that both a highly responsive and accurate system can beprovided for tracking at close ranges while moving rapidly over roughterrain as well as accommodating therelatively slight deviationsencountered when long range tracking from a stationary vehicle isrequired.

For example, it is apparent that any control and stabilization systemfor the weapon of a vehicle must be able to execute maximum excursionsof the weapon within a minimal time interval in order to achieve anattack advantage while at the same time being able to track a distanttarget at extremely low rates which may be on the order of 0.15mils/sec. Further, under such extremely low tracking conditions it isapparent that accuracy is of utmost importance when deviations due to anuneven terrain cause major effects in the orientation of the weapon.

Even though different inertias, structural resiliences, and dampingratios are inherent in the mechanical construction of the hull andturret of the vehicle and require some difference in the controlparameters of each system in order to obtain optimum performance, otherthan for differences in electrical gains and mechanical gear reductions,the control and stabilization systems for the two axes are essentiallythe same.

Prior art systems of control for the stabilization of a tank weaponinclude the R. J. Barlow et al, US. Pat. No. 3,405,599 entitled WeaponStabilization System which shows the utilization of gun and hull gyrosfor stabilization of the weapon in azimuth, and gun and turret gyros forstabilization in elevation. Integration and differentiation of the gyrosignals are employed to obtain position and acceleration signals whichare combined in a particular manner for control of a servo valve, inturn controlling fluid flow to the stabilizer for the respective axes.Such system is similar in showing compatibility with manual controlhandles, however, such control is effected in the hydraulic portion ofthe system wherein a synchronizer unit is employed and an overridingeffect is obtained to control the fluid flow to the actuator mechanism.Thus such system may be described as an alternate type of system whereincontrol of the actuator is either by conventional hydraulic flowtechniques or in alternate periods under the automatic control of theelectromechanical servo system.

In the apparatus of the instant invention a pair of gyros are similarlyemployed for each axis of stabilization being mounted respectively onthe weapon cradle and turret and the weapon cradle and hull of thevehicle, each gyro developing either a position or acceleration signalin addition to the directly available rate signal for a combined controlof the servo valve directing fluid flow to a hydraulic motor. Manualinput is supplied by a potentiometer coupled to the gunners controlhandle, providing the command signal to the servo loop and beingcontinuously connected in the loop when the weapon is in a stabilizationcondition.

A position transducer coupled to the second stage of the servo valvegenerates an electrical signal proportional to the displacement of thevalve spool and a tachometer coupled to the hydraulic motor provides anelectrical signal proportional to the angular rate of same, both signalsbeing utilized in feedback, as a portion of the servo loop.

Thus essentially the rate gyros mounted on the gun cradle, by means ofintegration circuits, provide an inertial positional frame of referenceas an input to the servo loop for stabilization of the weapon in eachaxis of motion and the manually operated potentiometers provide commandsignals for correcting the orientation of the weapon and for acquiringnew targets. The various feedback elements mentioned and the rate gyrosmounted on both the hull and the turret as supporting structure, serveto alter the characteristics of the servo loop to achieve optimumperformance.

in addition a drift correction signal is continuously applied as aninputto each servo system, being developed from a potentiometerintermittently coupled to the driving element of the servo loop at theoption of the operator to correct for hysteresis, friction, electricalimbalances and the like.

Additionally in lieu of operating in the stabilized mode, the system iscompatible with a power control and manual mode of operation, the formerproviding hydraulic actuation of the drive motors by way of fluidcoupling between hydraulic flow control valves contained in the gunnerscontrol and the respective drive motors, while in the manual mode directengagement with the traverse and elevation mechanism is possible by useof suitable gearing, no-back clutch elements and hand cranks.

Therefore it is one object of this invention to provide an improvedstabilization system which includes inherent synchronization betweenmanually applied inputs and the closed loop control system.

It is another object of this invention to provide an improvedstabilization system for a vehicle mounted weapon system having improvedtarget acquiring capabilities allowing the rapid slewing of the weaponto position and the laying on of the target without overshootmg.

It is another object of this invention to provide an improved weaponstabilization system in which a very high gain position loop isprovided, being accommodated by the utilization of components whichprovide improved damping.

It is a further object of this invention to provide an improvedstabilization system having very high gain and feedback for improveddamping, in which additional inertial signal members are utilized tomodify dynamic response of the system in order to reduce transienterrors.

It is a still further object of this invention to provide a weaponstabilization system including drift control mechanism therein whichalleviates a manual function of the gunner and provides a system havingimproved accuracy.

To the accomplishment of the foregoing and related ends, the invention,then, comprises the features hereinafter fully described, the followingdescription and the annexed drawings setting forth in detail certainillustrative embodiments of the invention, these being indicative,however, of but a few of the various ways in which the principles of theinvention may be employed.

In the drawings:

FIG. 1 is a partial perspective view of a vehicle equipped with theapparatus of this invention showing a weapon positionable in traverseand elevation;

FIG. 2 is a simplified schematic showing in block diagram form of oneaxis of stabilization for the control system;

FIG. 3 is a schematic showing in block diagram form of the completecontrol system for stabilization of a weapon in elevation and traverse;and

FIG. 4 is a schematic showing in block diagram form of the mechanicaland hydraulic arrangement employed in conjunction with the stabilizationsystem.

Referring now to the FIG. 1 perspective view there is shown a vehicle10, equipped with the weapon 11 under stabilization, consisting of aturret structure 12 and hull structure 13. The weapon 11 is capable ofbeing positioned in elevation with respect to the turret l2 and theturret is in turn rotatable with respect to the hull 13 for positioningin traverse, the combined movement providing orientation of the weapon11 with respect to a remote target. The turret and hull of the vehiclecomprise the supporting structure for the weapon and are movable as aunit under the conventional drive system of the vehicle 10, operatedunder control of the driver for movement in any direction over theterrain, either directly at the target or at any angle of attack withrespect thereto.

In a conventional arrangement the weapon 1! is mounted in a cradle M forpivotal movement with respect to the turret R2 of the vehicle and iscapable of limited arcuate movement. In this embodiment the cradle 14 issupported by a trunnion l6 journalled in the turret and in turn supportsthe weapon ll thereon. The cradle 14 further supports the weapon gyros18, 19 for movement with the cradle, the gyros being oriented to beresponsive to the elevational and traverse movements of the weapon 11.Also mounted on the cradle is a gear segment 20 which is engaged by theoutput pinion of a gear box containing a hydraulic drive motor, in turnreceiving fluid impetus from the stabilization system or by way ofmanually introduced flow as will be described in greater detailhereinafter. In a third and fully mechanical mode of operation, theoutput pinion may be engaged by a manually operable hand wheel through ano-back mechanism and appropriate gear reduction.

Similarly the turret 12 of the vehicle is mounted on the hull 13 forrotation in traverse about a substantially vertical axis in aconventional manner, the movement mechanism including a ring gear andhydraulic motor driven gearbox and output pinion which receives fluidflow through a second stabilization system in either the automatic ormanually controlled modes of operation previously described. Stillfurther a traverse hand crank and suitable mechanical driving mechanismprovide manual control over the traverse motion of the turret 12.

The gyros 18, 19 mounted for movement with the cradle 14 may beconventional units providing electrical signal outputs related to themovement of the structure on which mounted, in this embodiment the gyros118, 19 being orthogonally oriented to provide indications in theelevation and traverse planes of motion and providing signals of therates of movement of the weapon Ill in each coordinate axis. The gyrosare interconnected with electronic circuitry forming a part of thestabilization system for control of movement of both the cradle l4 andturret l2 and serve to maintain the orientation of the weapon 11 withrespect to a position in space selected by the gunner of the vehicle 10.

The gunner provides such orientation commands by the movement of controlhandles which are mechanically linked with the hydraulic system formanually controlling the flow of fluid to the respective drive motorsand simultaneously to potentiometers for develop ing electrical signalsfor alternate control from the stabilization system. Such controlelements are depicted schematically in FIGS. 2-4 but it will be clearthat any suitable mechanism and control devices may be employed toperform this function.

In the stabilized mode, of operation by virtue of suitable interlocks,the displacement of the control handles in each axis provides an outputfrom only the electrical control elements, i.e., the potentiometers,which elements command a proportional velocity for the control system.The gunner in looking through his sight recognizes any displacementbetween his line of sight and the desired target and displaces hiscontrol handles accordingly for reorientation of the stabilizationsystem, by rotation of a handle in the direction he wishes to displacethe line of sight in traverse and by tipping same in the direction hewishes to displace the line of sight in elevation.

While the rate gyros mounted on the weapon cradle 14 are the primaryelements for providing stabilization of the weapon 11 in an inertialframe of reference, rate gyros are mounted on the turret and hull of thevehicle respectively for providing additional inputs to the individualservo drive systems for the respective axes of control, in accommodationof the movement of the supporting structure of the vehicle 10 overterrain as directed by the driver. It is desired that the stabilizationsystem provide extremely high gain for rapid and responsive movement ofthe weapon 11 and the signals derived from the rate gyros on thesupporting structure are applied as inputs to the stabilization systemto improve the response of same in compatibility with maintainingaccuracy for the servo system.

The turret and hull gyros are mounted on suitable portions of thevehicle 10 and are also of the rate gyro type providing electricaloutput signals representative of the rate of movement of the portions ofthe vehicle in the elevation and traverse planes respectively. Theserate gyros are also electrically interconnected with the stabilizationsystem and are operative during the stabilized mode of operation of thevehicle.

Referring now to the FIG. 2 simplified showing of the stabilizationsystem there are indicated the essential elements forming the traverseaxis of stabilization. Included in this showing are the controlpotentiometer 24, being that device coupled to the gunners controlhandles which provides a desired command signal for the weapon to allowthe gunner to track the target. The output of the control potentiometer24 is a signal indicative of the desired rate of movement of the weapon11 and is applied to first and second combiner units 25, 26 which serveto algebraically add applied signals.

Position feedback for the stabilization system is developed from theweapon gyro 27, this being one of the rate gyros l8, 19 mounted on theweapon cradle 14 and providing a rate signal output as the second signalapplied to the first combiner unit 25. The combined signal output isthen applied to an integrator circuit 28 to provide a signalproportional to the angular error displacement of the weapon 11 in spacefrom the commanded line of orientation, such-signal then being appliedvia line 29 to the main combining unit 30 for development of the signalapplied on line 31 to the servo valve 32 for control of the hydraulicmotor driving the turret in traverse.

An LVDT 34 (linear variable differential transformer) serves as a sensorfor the servo valve 32 being mounted on the servo valve housing togenerate an electrical signal proportional to the displacement of thesecond stage spool, such signal being applied as one input on line 35 tothe second combiner unit 26. Further feedback for the servo loop isdeveloped in a tachometer 36 coupled to the hydraulic motor which servesas the servoactuator, generating an electrical signal proportional tothe angular rate of displacement of the hydraulic motor, such signalbeing applied as one input to athird combiner unit 38. Also in the servosystem is the hull gyro 39 being a rate gyro mounted on the vehicle togenerate an electrical signal proportional to the angular rate ofdisplacement in space of that structure, such signal being applied asthe second input to the third combiner unit 38. As will be described ingreater detail the tachometer 36 and hull gyro 39 signals are applied inopposition so that a difference signal on line 40 is obtained, thissignal being applied to a differentiating circuit 41 to develop anacceleration signal on line 42 in turn applied to the main combiner unit30 for development of the control signal for the servo valve 32. Thedifference signal on line 40 is also applied as one input to the secondcombiner unit 26 thereby developing a resultant velocity signal on line44 for application to the main combiner unit 30, such resultant signalbeing a function of the difference between the velocity of the structureon which the gyro 39 is mounted and the velocity of the hydraulic servoactuator.

The fourth input to the main combiner unit 30 is the drift signal online 45 developed from the drift potentiometer 46 providing theautomatic drift control which compensates for offsets and changes in thenull of the system components.

Thus, in operation of the stabilization system the gunner looks throughhis sight and recognizes displacement between the line of sight and thedesired target. He displaces his control handles and thus the controlpotentiometer 24 to command proportional velocity of the control systemasa correction for the orientation of the weapon 11. The output of thepotentiometer 24 is shaped to provide low sensitivity around center,allowing the gunner to track a moving target accurately and to lay on astationary target without overshooting. At either end of travel of thepotentiometer 24, sensitivity is progressively increased so that thegunner can rapidly slew the system to acquire a target.

To affect the necessary velocity commanded by the control potentiometer24 the servo valve 32 must be displaced the proper amount to provide thedesired flow to the hydraulic motor. The resultant rotation of the motorby way of mechanical coupling with the ring gear coupled to the turret12 will drive the latter at the desired speed to provide the correction.The LVDT 34 on the servo valve 32 is an electrical position sensorproviding an output voltage proportional to the direction and magnitudeof the flow from the servo valve 32. The tachometer 36 mounted on thehydraulic motor provides an output proportional to the direction ofrotation and angular velocity of the motor. Both are in the feedbackloop and provide voltages to resist motion of the system, being combinedin combiner units 38 and 26 to provide a velocity signal on line 44. Thevoltage from the control potentiometer 24 which is also directed tocombiner 26 must be calibrated to be equal to the sum of these twosignals at the desired system velocity in order to achieve equilibrium.Additionally such voltage from the control potentiometer 24 must also beequal to the output of the weapon gyro 27 so that the system can berepositioned at the desired rate of change. In this manner the gunnersinputs are synchronized with the control system.

Disturbances of the hull 13 due to steering and suspension inputs due tomovement over terrain tend to cause the line of sight to be displacedfrom the target and in order for the stabilization system to accommodatethis, the turret l2, and the cradle 14 in its own stabilization system,must be moved at a velocity equal and opposite to these inputs. In orderto accomplish this and to obtain a system with a high degree of staticaccuracy, the voltage output from the rate gyro 27 mounted on the cradleis electrically integrated to provide a reference position in spaceabout which the system operates. It is desirable also to select thesystem components so that the resultant position loop operates stably atthe highest possible gain, this being necessary since the position errorrequired to produce a velocity of the servo actuator is inverselyproportional to the gain of the position loop.

To further aid in increasing the system gain additional components areprovided to improve the damping. These include the LVDT 34 on the secondstage of the servo valve 32 and the tachometer 36 mounted on thehydraulic motor, the former providing an accurate linear long strokevalve with extremely high pressure gain while the output of thetachometer 36 is utilized in feedback both in a direct velocity mode andby differentiating the velocity signal to provide a voltage proportionalto the acceleration of the motor. The effect of these compensatingfeedbacks is to allow the gain of the position loop to be increasedthereby improving the static accuracy of the system but at the expenseof a reduction of the systems dynamic response.

The reduced dynamic response causes transient errors that are greaterthan desired and in order to reduce these errors to an acceptable level,additional rate gyros mounted on the hull and turret are utilized. Therate gyro 39 on the hull senses the angular velocity of the hull 13 inthe plane of the ring gear as a result of steering inputs from thedriver. The rate gyro in the turret senses the angular velocity of theturret 12 in the plane of the cradle as a result of pitch or roll inputsfrom the suspension and terrain.

Thus in FIG. 2 the output voltage from the hull gyro 39 is calibratedsuch that disturbances of the vehicle 10 generate voltages which areequal to the sum of the LVDT 34 and tachometer 36 outputs when thehydraulic motor rotates its output member at a velocity equal andopposite to the disturbing velocity. in addition, the hull gyro 39signal is added to the tachometer 36 signal in such a manner as toeliminate the effects of the acceleration feedback as a result ofvehicle disturbance. It does not theoretically require a steady stateerror in the position of the weapon gyro 27 to produce the requiredresponse. Instead, the open loop velocity and acceleration commands fromthe additional hull gyro 39 performs this function. It is only necessaryfor the position loop to contend dynamically with those errors in thesystem due to miscalibration, systems dynamics, and the various systemnonlinearities and to provide the necessary static accuracy.

The automatic drift control introduced by the drift potentiometer 46 isutilized to accommodate for the hysteresis and friction in the weapongyros and the offsets in the demodulators and integrators which causethe system to drift from the desired line of sight. The automatic driftcontrol consists of an appropriate gunner operated on-off circuit, thedrift potentiometers 46 and a solenoid operated brake and clutchmechanism. In operation when the vehicle comes to rest, the operator maycause energization of the clutch and engagement of the potentiometer 46with the output shaft of the hydraulic motor for a limited period oftime by pressing the reset button. If drifting of the system occursduring this period of time, any motor rotation will be coupled to thedrift potentiometer 46 to generate a signal which opposes that signalwhich caused the drift. Since the output of the potentiometer 46 iscontinuously coupled into the main combiner unit 30, the motor will cometo rest when the signals are of equal magnitude. Upon releasing thereset button the clutch and the potentiometer 46 will be mechanicallylocked in this position by a spring loaded brake. Under drift controlthe hydraulic motor and drift potentiometer 46 form an additionalintegrator in the system which balances out any drift and thenaccurately holds this balancing voltage until the next time the driftcontrol is operated.

Referring now to the block diagram of FIG. 3, an understanding of thecomplete stabilization system for a vehicle mounted weapon may beobtained. The affects upon the system are indicated by the blockslabeled gunner 48, driver 49 and terrain 50, the latter two providinginputs via the steering 51 and suspension 52 for the vehicle to the hull54, in turn rotatably mounting the turret 55 and the latter the cradle56, for movement of the weapon 57. This also moves the sight 58 whichprovides a means for feedback to the gunner 48 as indicated by line 59.The gunner 48 independently maneuvers the elevation and traversecontrols 60, 61, these being the potentiometers which provideproportional velocity commands while the hull gyro 62, turret gyro 64.and cradle gyros 65, 66 provide continuous feedback signalsrepresentative of motion of the respective elements as affected. Thecradle motor 67 as directed by servo valve 68 and the turret motor 69 asdirected by its servo valve 70 are mechanically coupled via appropriatereducer mechanisms 71, 72 respectively, to provide the impetus to thecradle 56 and turret 55.

In the elevation axis of stabilization, with corresponding elements inthe traverse axis indicated by the same reference numeral with thesubscripts b, the valve position sensor 74a provides the signalproportional to the flow magnitude through the servo valve 68 and atachometer 75a is coupled to the hydraulic motor 67 to provide theangular velocity signals. An integrator 76a and differentiating circuit77a receive inputs as shown utilizing appropriate combiner units 78a,79a, 80a, 81a in the manner similar to that set forth in the descriptionof the FIG. 2 simplified showing of one axis of the stabilizationsystem.

The automatic drift control is included independently in each axis ofstabilization comprising the drift potentiometer 82a providing acorrection signal, a clutch 84a coupling the shaft of the potentiometer82a with the motor 67 output shaft, a solenoid 85a for actuating theclutch 84a and a manually operated reset button. The combiner units78a-81a indicated in the FIG. 3 showing of the invention are onlyslightly modified from those depicted in the FIG. 2 simplified schematicof the system but the same function obtains, i.e., the tachometer 75aand turret gyro 64 are combined in opposition in combiner unit 81a whilethe output of the drift potentiometer 82a is directed to the integratorcircuit 76a via combiner unit 780 prior to application to the maincombiner unit 88a, such signal variations being minor and readilyaccommodated by suitable impedance networks and the like.

Thus, it may be seen that when in the stabilization mode the orientationof the weapon 57 may be maintained in spite of driver 49 introduced orterrain 50 introduced effects upon the disposition of same and may becontinuously altered by the gunner 48 who applies a visual correction tothe system. It is also to be noted that the stabilization system iscompatible with a completely mechanical mode of operation fororientation of the weapon 57 or a hydromechanical mode of operation forbackup or auxiliary purposes whereby the gunner 48 can manually orientthe weapon as desired.

Referring to FIG. 4 showing of the mechanical and electrohydraulicportion of the control system, the same control handles 90 coupled tothe control potenti ometer 24 of FIG. 2 and the elevation control 60 andtraverse control 61 of FIG. 3 are mechanically coupled to the traversecontrol valve 91 and the elevation control valve 92 providing fluid flowto the respective hydraulic motors 93a, b. By means of appropriateclutches 94a, b and gear reducers 95a, b output motion can be suppliedto the ring gear 96 for the turret 12 of the vehicle 10 and to the gearsector 97 for controlling the elevational orientation of the cradle 14and thus the weapon 11 mounted thereon.

Power for the system is obtained from the vehicle DC supply 100 by meansof a power relay 101 for driving a DC motor 102, in turn actuating apump 103. A pressure relief valve 104, accumulator 105, pressureregulator 106 and pressure switch 107 are utilized in a conventionalmanner to provide fluid to the selector valve 108, in turn coupled tothe control handles 90 and as indicated to the servo valves 68, 70 forthe stabilization system.

A pair of gunners palm switches 110a, b are provided for control ofsolenoid valves 111a, b, in turn controlling the actuation of clutches112a, b for selecting the hydromechanical or mechanical modes fordriving the weapon. The latter system includes a pair of hand cranks114a, b for the traverse and elevation mechanisms respectively, beingcoupled through noback devices 115a, b and the solenoid actuatedclutches 1120, b for drive of the reducer mechanisms 95a, b and thus thering gear 96 and gear sector 97 for movement of the weapon.

ln the hydraulic power control mode of operation displacement of thecontrol handles 90 in each axis operates the hydraulic valves 91, 92having shaped metering orifices providing an output similar to that ofthe potentiometers in the elevation and traverse controls 60, 61. In theclosed center four-way hydraulic valves 91, 92 the rate of change ofmetering area around center is verylow allowing the gunner to track themoving target accurately and to lay on a stationary target withoutovershooting. The rate .of change of .metering area at the ends of thevalves travel is progressively increased so that the gunner can rapidlyslew the system to initially acquire a target or change to a differenttarget. By way of the clutches 94a, b and reducers 95a, b, the axialpiston hydraulic motors 93a, b operate the turret and cradle .atvelocities proportional to the control handles displacement in responseto the gunners inputs.

When the gunner desires to change the line of sight he depresses thepalm switches 11011, b which are an integral part of the control handles90 to selectively operate the solenoid valves llla, b and engage eitheror both of the hydraulically operated clutches 94a, b. These clutches94a, b engage the hydraulic motors 93a, b with the gear reducers 95a, band the clutches 1112a, b disengage theno-backs 115a, b and hand cranks114a, b so that the hydraulic motors 93a, b can then drive the gearsector 97 or ring gear 96 as a function of control valve displacementwith the clutch acting as a safety overload device.

In the manual mode of operation of the system when the palm switches110a, b are not actuated, a spring in the clutches 94a, b disengages thehydraulic motors 93a, b from the gear reducers 950, b and engages theno-backs 115a, b and hand cranks lllda, b. The nobacks 115a, b act as abrake to ground preventing the output from reversibly driving the handcranks 114a, b and the clutches 112a, b as overload safety devices. Thehand cranks 114a, b allow the gunner to accurately position either theturret or cradle but are limited in speed capabilities by the operatorsphysical output power.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. Apparatus for stabilization with respect to an inertial referenceaxis of a movable member mounted on supporting structure subject torandom deviations from a predetermined aligned position comprising arate gyro mounted on said movable member for developing electricalsignals representative of the rate of movement of said member in theelevational plane, means for integrating the electrical signals of saidrate gyro to develop position signals representative of the dispositionof said element in the elevational plane with respect to an inertialaxis of reference, a second rate gyro mounted on said supportingstructure for developing electrical signals representative of the rateof movement of said structure in the elevational plane, a motor forimparting motion to said movable member in response to fluid flow at arate proportional to a control signal, a tachometer coupled to saidmotor for providing electrical signals representative of the rate ofrotation of same, means for differentially combining said tachometersignals and said second rate gyro signals to produce a resultant signal,means for differentiating said resultant signal to provide anacceleration signal, a servo valve for controlling fluid flow inresponse to electrical signals, a transducer coupled to the second stageof said servo valve to provide signals representative of thedisplacement of same, and means for combining said resultant signal,said transducer signal, said acceleration signal and said positionsignals to provide a combined signal for control of said servo valve.

2. Apparatus as set forth in claim 1 further including a manuallyadjustable control potentiometer for developing electrical signalsrepresentative of desired rate of movement of said movable element,means for combining said potentiometer signals with the signals of saidfirst rate gyro for application to said integrating means, saidpotentiometer signals being separately applied to said last-namedcombining means to introduce a manual adjustment signal in the combinedsignal applied to said servo valve.

3. Apparatus as set forth in claim 1 further including a secondadjustable potentiometer for developing drift signals for correction ofoffset errors, friction effects and the like in the stabilizationsystem, said drift signals being applied to said combining means forsummation with said combined signal for control of said servo valve.

4. Apparatus for stabilization of a member movable with respect tosupporting structure, comprising a motor for imparting movement to saidmember in response to an applied input, a first rate gyro mounted formovement with said member for developing electrical signalsrepresentative of such movement, means for integrating the electricaloutput of said first rate gyro to provide signals representative of theposition of said member, a second rate gyro mounted on said supportingstructure for developing electrical signals representative of the rateof movement of said supporting structure due to external influences,said second rate gyro being oriented'to be responsive to influencesaffecting the position of said movable member in the manner sensed bysaid first rate gyro, means for manually introducing electrical commandsignals for control of movement of said movable member, and means forcombining said command, position and rate signals to produce a combinedelectrical output signal for control of said motor.

5. Apparatus as set forth in claim 4 further including a tachometercoupled to said motor for providing electrical output signalsrepresentative of the rate of rotation of same, said tachometer outputsignals being applied to said combining means for control of the motorrunning characteristics.

6. Apparatus as set forth in claim 5 wherein said motor is a hydraulicmotor and further including a servo valve for controlling fluid flow tosaid motor as a function of the combined signal of said combining means.

7. Apparatus as set forth in claim 6 further including a transducercoupled to said servo valve for monitoring the positioning of same, saidtransducer providing an electrical signal representative thereof, andfurther in cluding means for coupling said transducer signal to saidcombining means.

8. Apparatus as set forth in claim 7 wherein said combining meanscomprises first means for combining said tachometer and said second rategyro signals, and second means for combining the output of said firstcombining means, said transducer signals and said manual command signalsfor application to said first named combining means.

9. Apparatus as set forth in claim 8 wherein said movable member is theweapon of a tank, mounted for movement in elevation in the tank turret,said turret in turn mounted for movement in traverse in the tank hull,said first rate gyro being operatively mounted on said weapon and saidsecond rate gyro being operatively mounted on said turret.

10. Apparatus as set forth in claim 9 further including third and fourthrate gyros respectively operatively mounted on said weapon and said hullfor monitoring movements of traverse, means for integrating the signalsof said third rate gyro, means for differentiating the signals of saidfourth rate gyro, a motor for controlling movement of said turret intraverse, means for introducing manual command signals for control ofsaid turret, and means for combining said turret command signals, saidintegrated signals and said differentiated signals for application tosaid turret motor for control of traverse movements.

11. A drift control mechanism for stabilization systems and the likewherein a closed loop servo maintains disposition of an object by meansof a motor driven, gyro stabilized, error compensating system,comprising means coupled to the motor for providing indications of theactuated and non-actuated conditions of the same, a transducer forproviding an electrical signal in response to a mechanical variation insame, normally disengaged coupling means for coupling said transducer tothe motor in response to an electrical signal, a manually operated resetbutton to engage said coupling means for sensing deviations of the motordue to offset error, drift and the like by driving said transducerthrough said coupling means and generating a signal opposing any signalcausing drift, means for locking said transducer in its position uponrelease of said manually operated reset button, and means continuouslyconnecting the electrical signal of said transducer to the errorcompensating system as a drift compensation signal.

12. The drift control mechanism as set forth in claim 11 wherein saidtransducer is a potentiometer and said coupling means is asolenoid-actuated clutch interconnecting the motor and saidpotentiometer.

1. Apparatus for stabilization with respect to an inertial referenceaxis of a movable member mounted on supporting structure subject torandom deviations from a predetermined aligned position comprising arate gyro mounted on said movable member for developing electricalsignals representative of the rate of movement of said member in theelevational plane, means for integrating the electrical signals of saidrate gyro to develop position signals representative of the dispositionof said element in the elevational plane with respect to an inertialaxis of reference, a second rate gyro mounted on said supportingstructure for developing electrical signals representative of the rateof movement of said structure in the elevational plane, a motor forimparting motion to said movable member in response to fluid flow at arate proportional to a control signal, a tachometer coupled to saidmotor for providing electrical signals representative of the rate ofrotation of same, means for differentially combining said tachometersignals and said second rate gyro signals to produce a resultant signal,means for differentiating said resultant signal to provide anacceleration signal, a servo valve for controlling fluid flow inresponse to electrical signals, a transducer coupled to the second stageof said servo valve to provide signals representative of thedisplacement of same, and means for combining said resultant signal,said transducer signal, said acceleration signal and said positionsignals to provide a combined signal for control of said servo valve. 2.Apparatus as set forth in claim 1 further including a manuallyadjustable control potentiometer for developing electrical signalsrepresentative of desired rate of movement of said movable element,means for combining said potentiometer signals with the signals of saidfirst rate gyro for application to said integrating means, saidpotentiometer signals being separately applied to said last-namedcombining means to introduce a manual adjustment signal in the combinedsignal applied to said servo valve.
 3. Apparatus as set forth in claim 1further including a second adjustable potentiometer for developing driftsignals for correction of offset errors, friction effects and the likein the stabilization system, said drift signals being applied to saidcombining means for summation with said combined signal for control ofsaid servo valve.
 4. Apparatus for stabilization of a member movablewith respect to supporting structure, comprising a motor for impartingmovement to said member in response to an applied input, a first rategyro mounted for movement with said member for developing electricalsignals representative of such movement, means for integrating theelectrical output of said first rate gyro to provide signalsrepresentative of the position of said member, a second rate gyromounted on said supporting structure for developing electrical signalsrepresentative of the rate of movement of said supporting structure dueto external influences, said second rate gyro being oriented to beresponsive to influences affecting the position of said movable memberin the manner sensed by said first rate gyro, means for manuallyintroducing electrical command signals for control of movement of saidmovable member, and means for combining said command, position and ratesignals to produce a combined electrical output signal for control ofsaid motor.
 5. Apparatus as set forth in claim 4 further including atachometer coupled To said motor for providing electrical output signalsrepresentative of the rate of rotation of same, said tachometer outputsignals being applied to said combining means for control of the motorrunning characteristics.
 6. Apparatus as set forth in claim 5 whereinsaid motor is a hydraulic motor and further including a servo valve forcontrolling fluid flow to said motor as a function of the combinedsignal of said combining means.
 7. Apparatus as set forth in claim 6further including a transducer coupled to said servo valve formonitoring the positioning of same, said transducer providing anelectrical signal representative thereof, and further including meansfor coupling said transducer signal to said combining means. 8.Apparatus as set forth in claim 7 wherein said combining means comprisesfirst means for combining said tachometer and said second rate gyrosignals, and second means for combining the output of said firstcombining means, said transducer signals and said manual command signalsfor application to said first named combining means.
 9. Apparatus as setforth in claim 8 wherein said movable member is the weapon of a tank,mounted for movement in elevation in the tank turret, said turret inturn mounted for movement in traverse in the tank hull, said first rategyro being operatively mounted on said weapon and said second rate gyrobeing operatively mounted on said turret.
 10. Apparatus as set forth inclaim 9 further including third and fourth rate gyros respectivelyoperatively mounted on said weapon and said hull for monitoringmovements of traverse, means for integrating the signals of said thirdrate gyro, means for differentiating the signals of said fourth rategyro, a motor for controlling movement of said turret in traverse, meansfor introducing manual command signals for control of said turret, andmeans for combining said turret command signals, said integrated signalsand said differentiated signals for application to said turret motor forcontrol of traverse movements.
 11. A drift control mechanism forstabilization systems and the like wherein a closed loop servo maintainsdisposition of an object by means of a motor driven, gyro stabilized,error compensating system, comprising means coupled to the motor forproviding indications of the actuated and non-actuated conditions of thesame, a transducer for providing an electrical signal in response to amechanical variation in same, normally disengaged coupling means forcoupling said transducer to the motor in response to an electricalsignal, a manually operated reset button to engage said coupling meansfor sensing deviations of the motor due to offset error, drift and thelike by driving said transducer through said coupling means andgenerating a signal opposing any signal causing drift, means for lockingsaid transducer in its position upon release of said manually operatedreset button, and means continuously connecting the electrical signal ofsaid transducer to the error compensating system as a drift compensationsignal.
 12. The drift control mechanism as set forth in claim 11 whereinsaid transducer is a potentiometer and said coupling means is asolenoid-actuated clutch interconnecting the motor and saidpotentiometer.